Power control for a channel with multiple formats in a communication system

ABSTRACT

Techniques to more efficiently control the transmit power for a data transmission that uses a number of formats (e.g., rates, transport formats). Different formats for a given data channel (e.g., transport channel) may require different target SNIRs to achieved a particular BLER. In one aspect, individual target BLER may be specified for each format of each data channel. In another aspect, various power control schemes are provided to achieve different target SNIRs for different formats. In a first power control scheme, multiple individual outer loops are maintained for multiple formats. For each format, its associated outer loop attempts to set the target SNIR such that the target BLER specified for that format is achieved. In a second power control scheme, multiple individual outer loops are maintained and the base station further applies different adjustments to the transmit power levels for different formats.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present application for patent is a Continuation and claims priorityto patent application Ser. No. 11/249,786, entitled “POWER CONTROL FOR ACHANNEL WITH MULTIPLE FORMATS IN A COMMUNICATION SYSTEM,” filed Oct. 12,2005, which claims priority to patent application Ser. No. 09/933,604,entitled “POWER CONTROL FOR A CHANNEL WITH MULTIPLE FORMATS IN ACOMMUNICATION SYSTEM” filed Aug. 20, 2001, granted as U.S. Pat. No.6,983,166, issued Jan. 3, 2006, hereby expressly incorporated byreference herein.

BACKGROUND

1. Field

The present invention relates generally to data communication, and morespecifically to techniques for controlling the transmit power of a datatransmission that uses multiple formats (e.g., rates, transport formats)as supported by a communication system using power control (e.g.,W-CDMA).

2. Background

In a wireless communication system, a user with a terminal (e.g., acellular phone) communicates with another user via transmissions on thedownlink and uplink through one or more base stations. The downlink(i.e., forward link) refers to transmission from the base station to theterminal, and the uplink (i.e., reverse link) refers to transmissionfrom the terminal to the base station. The downlink and uplink aretypically allocated different frequencies.

In a Code Division Multiple Access (CDMA) system, the total transmitpower available for a base station is typically indicative of the totaldownlink capacity for that base station since data may be concurrentlytransmitted to a number of terminals over the same frequency band. Aportion of the total available transmit power is allocated to eachactive terminal such that the aggregate transmit power for all activeterminals is less than or equal to the total available transmit power.

To maximize the downlink capacity, a power control mechanism istypically used to minimize power consumption and interference whilemaintaining the desired level of performance. Conventionally, this powercontrol mechanism is implemented with two power control loops. The firstpower control loop (often referred to as an “inner” power control loop,or simply, the inner loop) adjusts the transmit power to each terminalsuch that the signal quality of the transmission received at theterminal (e.g., as measured by a signal-to-noise-plus-interference ratio(SNIR)) is maintained at a particular target SNIR. This target SNIR isoften referred to as the power control setpoint (or simply, thesetpoint). The second power control loop (often referred to as an“outer” power control loop, or simply, the outer loop) adjusts thetarget SNIR such that the desired level of performance (e.g., asmeasured by a particular target block error rate (BLER), frame errorrate (FER), or bit error rate (BER)) is maintained. By minimizing theamount of transmit power while maintaining the target BLER, increasedsystem capacity and reduced delays in serving users can be achieved.

A W-CDMA system supports data transmission on one or more transportchannels, and one or more transport formats may be used for eachtransport channel. Each transport format defines various processingparameters such as the transmission time interval (TTI) over which thetransport format applies, the size of each transport block of data, thenumber of transport blocks within each TTI, the coding scheme to be usedfor the TTI, and so on. The use of multiple transport formats allowsdifferent types or rates of data to be transmitted over a singletransport channel.

The W-CDMA standard currently permits one target BLER to be specified bythe base station for each transport channel, regardless of the number oftransport formats that may be selected for use for the transportchannel. Each transport format may be associated with a different codeblock length, which may in turn require a different target SNIR toachieve the target BLER. (For W-CDMA, the code block length isdetermined by the transport block size, which is specified by thetransport format.) In W-CDMA, one or more transport channels aremultiplexed together in a single physical channel, whose transmit poweris adjusted through power control. Using the conventional power controlmechanism, the inner power control loop would adjust the target SNIRbased on the received transport blocks to achieve the target BLER orbetter for each transport channel.

Since different transport formats may require different target SNIRs toachieve the target BLER, the average transmit power for the physicalchannel may fluctuate depending on the specific sequence of transportformats selected for use in the constituent transport channel(s) (i.e.,the relative frequency of the transport formats and their ordering). Andsince the outer and inner loops take some amount of time to converge,each time the transport format is changed, a transient occurs until theloops converge on the target SNIR for the new transport format. Duringthis transient time, the actual BLER may be much greater or less thanthe target BLER, which would then result in degraded performance andlower system capacity.

There is therefore a need in the art for an improved power controlmechanism for a (e.g., W-CDMA) communication system capable oftransmitting data on one or more transport channels using multipletransport formats.

SUMMARY

Aspects of the invention provide techniques to more efficiently controlthe transmit power for a data transmission over a power-controlledchannel that includes one or many data channels, with each data channelbeing associated with one or more formats (e.g., rates, transportformats as defined in W-CDMA, and so on). As used herein, a data channelrefers to any signaling path for information (e.g., traffic or control)for which there is one or more associated data integrity specificationson the information (e.g., BLER, FER, and/or BER specification). Theinvention recognizes that different formats for a given data channel(e.g., a transport channel in W-CDMA) may require different target SNIRsto achieved a particular BLER. Various schemes are provided herein toeffectively treat these different formats as “individual” transmissionswith their own performance requirements, while reducing the overalltransmit power for the data transmission. For clarity, various aspectsand embodiments are described specifically for W-CDMA whereby multipletransport formats may be defined for each transport channel, and one ormore transport channels are multiplexed onto a physical channel.However, the techniques described herein may also be applied to othersystems whereby multiple formats are defined for each data channel, andone or more data channels are multiplexed onto a single power-controlledchannel.

In one aspect, a particular target BLER may be specified for eachtransport format of each transport channel used for a data transmission,instead of a single target BLER for all transport formats of eachtransport channel. If N transport formats are available for use for agiven transport channel, then up to N target BLERs may be specified forthe transport channel.

In another aspect, various power control schemes are provided to achievedifferent target SNIRs for different transport formats. These schemesmay be used to achieve different target BLERs specified for differenttransport formats (i.e., different code block lengths), which typicallyrequire different target SNIRs. These schemes may also be used if asingle target BLER is specified for all transport formats of a giventransport channel, since different transport formats may requiredifferent target SNIRs to achieve the same target BLER.

In a first power control scheme for achieving different target SNIRs fordifferent transport formats, multiple individual outer loops aremaintained for multiple transport formats. For each transport format,its associated outer loop attempts to set the target SNIR such that thetarget BLER specified for that transport format is achieved. Themultiple individual outer loops would then form an overall outer loopthat operates in conjunction with the (common) inner loop to derive theproper power control commands for all transport formats.

In a second power control scheme for achieving different target SNIRsfor different transport formats, multiple individual outer loops aremaintained for multiple transport formats, and the base station furtherapplies different adjustments to the transmit power levels for differenttransport formats. The base station has knowledge of the specifictransport format(s) that will be used for an upcoming transmission timeinterval (TTI) and can also participate in the power control byadjusting the transmit power for the data transmission based on theactual transport format(s) selected for use.

In one embodiment of the second scheme, the base station is providedwith a table of power offsets for the available transport formats, whichcan be computed based on the relative difference in the target SNIRsrequired for the transport formats to achieve their target BLERs. Foreach TTI, the base station selects one or more transport formats for usefor the TTI, retrieves from the table the power offset for each selectedtransport format, and transmits at a power level determined in part bythe power offset(s) for the selected transport format(s). The basestation's (transport format dependent) power adjustment may be made onlyto the data portion of a transmitted frame while the transmit powerlevel for the remaining portion of the transmitted frame can bemaintained (i.e., not adjusted based on transport format).

In another embodiment of the second scheme, the terminal assists in thedetermination of the power offsets (which are updated via a third powercontrol loop) and provides updates for the power offsets to the basestation based on a particular update scheme (e.g., periodically, asnecessary, upon fulfillment of one or more conditions, and so on).

The various aspects and embodiments of the invention may be applied toany communication system that uses multiple formats for a singlepower-controlled channel. Multiple formats or rates may be supported bythe use of multiple transport formats in W-CDMA and by other mechanismsin other CDMA standards. The techniques described herein may also beapplied to the uplink as well as the downlink.

The invention further provides methods, power control mechanisms,apparatus, and other elements that implement various aspects,embodiments, and features of the invention, as described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a diagram of a wireless communication system that supports anumber of users and is capable of implementing various aspects andembodiments of the invention;

FIGS. 2A and 2B are diagrams of the signal processing at a base stationand a terminal, respectively, for a downlink data transmission inaccordance with the W-CDMA standard;

FIGS. 3A and 3B illustrate two different transport formats that may beused for two different transport channels;

FIG. 4 is a diagram of a frame format and a slot format for a downlinkDPCH defined by the W-CDMA standard;

FIG. 5 is a diagram of a downlink power control mechanism capable ofimplementing various aspects and embodiments of the invention;

FIG. 6 illustrates a first power control scheme whereby multipleindividual outer loops are maintained to control the transmit power of adata transmission that uses multiple transport formats;

FIG. 7 is a flow diagram of an embodiment of a process performed at theterminal to maintain a number of individual outer loops for a number oftransport formats based on the first power control scheme;

FIG. 8 illustrates a second power control scheme whereby multipleindividual outer loops are maintained and transport format dependentpower adjustment is made at the base station;

FIG. 9 is a diagram illustrating a specific implementation of the secondpower control scheme;

FIG. 10 is a diagram illustrating an embodiment of a third power controlloop to maintain power offsets for multiple transport formats;

FIG. 11 is a flow diagram of an embodiment of a process performed at theterminal to maintain a number of individual outer loops for a number oftransport formats based on the second power control scheme; and

FIGS. 12 and 13 are block diagrams of an embodiment of the base stationand the terminal, respectively.

DETAILED DESCRIPTION

FIG. 1 is a diagram of a wireless communication system 100 that supportsa number of users and is capable of implementing various aspects andembodiments of the invention. System 100 includes a number of basestations 104 that provide coverage for a number of geographic regions102. A base station is also referred to as a base transceiver system(BTS) (in IS-95), an access point (in IS-856), or a Node B (in W-CDMA).The base station and/or its coverage area are also often referred to asa cell. System 100 may be designed to implement any combination of oneor more CDMA standards such as IS-95, cdma2000, IS-856, W-CDMA, andother standards. These standards are known in the art and incorporatedherein by reference.

As shown in FIG. 1, various terminals 106 are dispersed throughout thesystem. A terminal is also referred to as a mobile station, an accessterminal (in IS-856), or a user equipment (UE) (in W-CDMA). In anembodiment, each terminal 106 may communicate with one or more basestations 104 on the downlink and uplink at any given moment, dependingon whether or not the terminal is active and whether or not it is insoft handoff. As shown in FIG. 1, base station 104 a communicates withterminals 106 a, 106 b, 106 c, and 106 d, and base station 104 bcommunicates with terminals 106 d, 106 e, and 106 f. Terminal 106 d isin soft handoff and concurrently communicates with base stations 104 aand 104 b.

In system 100, a system controller 102 couples to base stations 104 andmay further couple to a public switched telephone network (PSTN) and/orone or more packet data serving node (PDSN). System controller 102provides coordination and control for the base stations coupled to it.System controller 102 further controls the routing of calls amongterminals 106, and between terminals 106 and the PDSN or other userscoupled to the PSTN (e.g., conventional telephones). System controller102 is often referred to as a base station controller (BSC) or a radionetwork controller (RNC).

FIG. 2A is a diagram of the signal processing at a base station for adownlink data transmission, in accordance with the W-CDMA standard. Theupper signaling layers of a W-CDMA system support data transmission onone or more transport channels to a specific terminal, with eachtransport channel being capable of carrying data for one or moreservices. These services may include voice, video, packet data, and soon, which are collectively referred to herein as “data”.

The data for each transport channel is processed based on one or moretransport formats selected for that transport channel. Each transportformat defines various processing parameters such as a transmission timeinterval (TTI) over which the transport format applies, the size of eachtransport block of data, the number of transport blocks within each TTI,the coding scheme to be used for the TTI, and so on. The TTI may bespecified as 10 msec, 20 msec, 40 msec, or 80 msec. Each TTI can be usedto transmit a transport block set having N_(B) equal-sized transportblocks, as specified by the transport format for the TTI. For eachtransport channel, the transport format can dynamically change from TTIto TTI, and the set of transport formats that may be used for thetransport channel is referred to as the transport format set.

As shown in FIG. 2A, the data for each transport channel is provided, inone or more transport blocks for each TTI, to a respective transportchannel processing section 210. Within each processing section 210, eachtransport block is used to calculate a set of cyclic redundancy check(CRC) bits, in block 212. The CRC bits are attached to the transportblock and are used at the terminal for block error detection. The one ormore CRC coded blocks for each TTI are then serially concatenatedtogether, in block 214. If the total number of bits after concatenationis greater than the maximum size of a code block, then the bits aresegmented into a number of (equal-sized) code blocks. The maximum codeblock size is determined by the particular coding scheme (e.g.,convolutional, Turbo, or no coding) selected for use for the currentTTI, which is specified by the transport format. Each code block is thencoded with the selected coding scheme or not coded at all, in block 216,to generate coded bits.

Rate matching is then performed on the coded bits in accordance with arate-matching attribute assigned by higher signaling layers andspecified by the transport format, in block 218. On the uplink, bits arerepeated or punctured (i.e., deleted) such that the number of bits to betransmitted matches the number of available bit positions. On thedownlink, unused bit positions are filled with discontinuoustransmission (DTX) bits, in block 220. The DTX bits indicate when atransmission should be turned off and are not actually transmitted.

The rate-matched bits for each TTI are then interleaved in accordancewith a particular interleaving scheme to provide time diversity, inblock 222. In accordance with the W-CDMA standard, the interleaving isperformed over the TTI, which can be selected as 10 msec, 20 msec, 40msec, or 80 msec. When the selected TTI is longer than 10 msec, the bitswithin the TTI are segmented and mapped onto consecutive transportchannel frames, in block 224. Each transport channel frame correspondsto the portion of the TTI that is to be transmitted over a (10 msec)physical channel radio frame period (or simply, a “frame”).

In W-CDMA, data to be transmitted to a particular terminal is processedas one or more transport channels at a higher signaling layer. Thetransport channels are then mapped to one or more physical channelsassigned to the terminal for a communication (e.g., a call). In W-CDMA,a downlink dedicated physical channel (downlink DPCH) is typicallyassigned to each terminal for the duration of a communication. Thedownlink DPCH is used to carry the transport channel data in atime-division multiplexed manner along with control data (e.g., pilot,power control information, and so on). The downlink DPCH may thus beviewed as a multiplex of a downlink dedicated physical data channel(DPDCH) and a downlink dedicated physical control channel (DPCCH), asdescribed below. The transport channel data is mapped only to the DPDCH,while the DPCCH includes the physical layer signaling information.

The transport channel frames from all active transport channelprocessing sections 210 are serially multiplexed into a coded compositetransport channel (CCTrCH), in block 232. DTX bits may then be insertedinto the multiplexed radio frames such that the number of bits to betransmitted matches the number of available bit positions on one or more“physical channels” to be used for the data transmission, in block 234.If more than one physical channel is used, then the bits are segmentedamong the physical channels, in block 236. The bits in each frame foreach physical channel are then further interleaved to provide additionaltime diversity, at block 238. The interleaved bits are then mapped tothe data portions of their respective physical channels, at block 240.The subsequent signal processing to generate a modulated signal suitablefor transmission from the base station to the terminal is known in theart and not described herein.

FIG. 2B is a diagram of the signal processing at a terminal for thedownlink data transmission, in accordance with the W-CDMA standard. Thesignal processing shown in FIG. 2B is complementary to that shown inFIG. 2A. Initially, the modulated signal is received, conditioned,digitized, and processed to provide symbols for each physical channelused for the data transmission. Each symbol has a particular resolution(e.g., 4-bit) and corresponds to a transmitted bit. The symbols in eachframe for each physical channel are de-interleaved, in block 252, andthe de-interleaved symbols from all physical channels are concatenated,in block 254. The symbols are then demultiplexed into various transportchannels, in block 258. The radio frames for each transport channel arethen provided to a respective transport channel processing section 260.

Within each transport channel processing section 260, the transportchannel radio frames are concatenated into transport block sets, inblock 262. Each transport block set includes one or more transportchannel radio frames a respective TTI. The symbols within each transportblock set are de-interleaved, in block 264, and non-transmitted symbolsare removed, in block 266. Inverse rate matching (or de-rate matching)is then performed to accumulate repeated symbols and insert “erasures”for punctured symbols, in block 268. Each coded block in the transportblock set is then decoded, in block 270, and the decoded blocks areconcatenated and segmented into one or more transport blocks, in block272. Each transport block is then checked for error using the CRC bitsattached to the transport block, in block 274. For each transportchannel, one or more decoded transport blocks are provided for each TTI.

FIGS. 3A and 3B illustrate two different transport formats that may beused for two different transport channels. As noted above, eachtransport channel may be associated with a respective transport formatset, which includes one or more transport formats available for use forthe transport channel. Each transport format defines, among otherparameters, the size of the transport block and the number of transportblocks in a TTI.

FIG. 3A illustrates a transport format set whereby one transport blockis transmitted for each TTI, with the transport blocks for differenttransport formats having different sizes. This transport format set maybe used, for example, for voice service whereby an adaptive multi-rate(AMR) speech coder may be used to provide a full rate (FR) frame, asilence descriptor (SID) frame, or a no-data (NULL or DTX) frame every20 msec depending on the speech contents. The TTI can then be selectedas 20 msec. FR frames are provided during periods of active speech, anda SID frame is typically sent once every 160 msec during periods ofsilence (i.e., pauses). In general, shorter transport blocks may be sentwhen there is no (or less) voice activity and longer transport blocksmay be sent when there is (more) voice activity. The NULL frame is sentduring periods of silence when SID is not sent.

FIG. 3B illustrates a transport format set whereby one or more transportblocks are transmitted for each TTI, with the transport blocks fordifferent transport formats having different sizes. This transportformat set may be used, for example, to support multiple services on agiven transport channel. For example, a non-realtime service (e.g.,packet data) may be multiplexed with a realtime service (e.g., voice).In this case, additional transport blocks may be used to support thenon-realtime service when and as needed.

The W-CDMA standard defines a channel structure capable of supporting anumber of users and designed for efficient transmission of various typesof data. As noted above, in accordance with the W-CDMA standard, data tobe transmitted to each terminal is processed as one or more transportchannels at a higher signaling layer, and the transport channel data isthen mapped to one or more physical channels assigned to the terminal.The transport channels support concurrent transmission of differenttypes of services (e.g., voice, video, packet data, and so on) for anumber of users.

In the W-CDMA system, a downlink DPCH is typically assigned to eachterminal for the duration of a communication. The downlink DPCH is usedto carry one or more transport channels and is characterized by thepossibility of fast data rate change (e.g., every 10 msec), fast powercontrol, and inherent addressing to a specific terminal. The downlinkDPCH is used to transmit user-specific data in a time-divisionmultiplexed manner along with control data.

FIG. 4 is a diagram of a frame format and a slot format for the downlinkDPCH, as defined by the W-CDMA standard. The data to be transmitted onthe downlink DPCH is partitioned into radio frames, with each radioframe being transmitted over a (10 msec) frame that comprises 15 slotslabeled as slot 0 through slot 14. Each slot is further partitioned intoa number of fields used to carry user-specific data, signaling, andpilot, or a combination thereof.

As shown in FIG. 4, for the downlink DPCH, each slot includes datafields 420 a and 420 b (Data1 and Data2), a transmit power control (TPC)field 422, a transport format combination indicator (TFCI) field 424,and a pilot field 426. Data fields 420 a and 420 b are used to senduser-specific data. TPC field 422 is used to send power controlinformation to direct the terminal to adjust its uplink transmit powereither up or down to achieve the desired uplink performance whileminimizing interference to other terminals. TFCI field 424 is used tosend information indicative of the transport format of the downlink DPCHand a downlink shared channel DSCH, if any, assigned to the terminal.And pilot field 426 is used to send a dedicated pilot for the downlink.

On the downlink, the capacity of each base station is limited by itstotal available transmit power. To provide the desired level ofperformance and maximize system capacity, the transmit power of eachdata transmission from the base station is typically controlled to be aslow as possible to reduce power consumption and interference whilemaintaining the desired level of performance (e.g., a particular targetBLER, FER, or BER). If the received signal quality as measured by thereceived signal-to-noise-plus-interference ratio (SNIR) at the terminalis too poor, then the likelihood of correctly decoding the datatransmission decreases and performance may be compromised (higher BLER).Conversely, if the received signal quality is too high, then thetransmit power level is likely to be too high and excessive amount oftransmit power may have been unnecessarily used for the datatransmission, which would then reduce system capacity and may furthercause extra interference to the transmissions from other base stations.

FIG. 5 is a diagram of a downlink power control mechanism 500 capable ofimplementing various aspects and embodiments of the invention. Powercontrol mechanism 500 includes an inner power control loop 510 thatoperates in conjunction with an outer power control loop 520.

Inner loop 510 is a (relatively) fast loop that attempts to maintain thesignal quality of a data transmission received at the terminal as closeas possible to a target SNIR (i.e., a setpoint). As shown in FIG. 5,inner loop 510 operates between the base station and the terminal, andone inner loop is typically maintained for each data transmission to beindependently power-controlled.

The inner loop adjustment for a particular data transmission istypically achieved by (1) measuring the signal quality of the datatransmission at the terminal (block 512), (2) comparing the receivedsignal quality (i.e., the received SNIR) against the target SNIR (block514), and (3) sending power control information back to the transmittingbase station. The signal quality measurement is typically made on apilot included in the data transmission. The power control informationmay be used by the base station to adjust its transmit power for thedata transmission, and may be in the form of an “UP” command to requestan increase in the transmit power or a “DOWN” command to request adecrease in the transmit power. The base station may adjust the transmitpower for the data transmission accordingly (block 516) each time itreceives the power control information. For the W-CDMA system, the powercontrol information may be sent as often as 1500 times per second (i.e.,one power control command for each slot), thus providing a relativelyfast response time for inner loop 510.

Due to path loss, fading, and possibly other phenomena in thecommunication channel (cloud 518), which typically varies over time,especially for a mobile terminal, the received SNIR at the terminalcontinually fluctuates. Inner loop 510 attempts to maintain the receivedSNIR at or near the target SNIR in the presence of changes in thecommunication channel.

Outer loop 520 is a (relatively) slower loop that continually adjuststhe target SNIR such that the desired level of performance is achievedfor the data transmission to the terminal. The desired level ofperformance is typically specified as a particular target BLER, althoughsome other performance criterion may also be used to adjust the targetSNIR. The target SNIR necessary to maintain a particular target BLER maychange depending on the conditions of the communication channel. Forexample, a fast fading channel may have a different SNIR target than aslow fading channel to maintain the same BLER.

The outer loop adjustment for the SNIR target is typically achieved by(1) receiving and processing the data transmission to recovertransmitted data blocks (or transport blocks), (2) determining thestatus of each received transport block (block 522) as being decodedcorrectly (good) or in error (erased), and (3) adjusting the target SNIR(block 524) based on the transport block status (and possibly along withother information, as described below). If a transport block is decodedcorrectly, then the received SNIR at the terminal is likely to be higherthan necessary and the target SNIR may be reduced slightly.Alternatively, if a transport block is decoded in error, then thereceived SNIR at the terminal is likely to be lower than necessary andthe target SNIR may be increased. In either scenario, inner loop 510will try to keep the received SNIR at the target SNIR provided by theouter loop.

By controlling the manner in which the target SNIR is adjusted,different power control characteristics and performance level may beobtained. For example, the target BLER may be adjusted by selecting theproper amount of upward adjustment (ΔUP) in the target SNIR for a badblock, the amount of downward adjustment (ΔDN) for a good block, therequired elapsed time between successive increases in the target SNIR,and so on. The target BLER (i.e., the long-term BLER) may be set asΔDN/(ΔDN+ΔUP). The magnitudes of ΔUP and ΔDN also determine theresponsiveness of the power control mechanism to sudden changes in thecommunication channel.

For the W-CDMA system, the terminal can estimate the received SNIR ofthe transmission on the downlink DPCH (or more specifically, the piloton the DPCCH). The terminal then compares the received SNIR to thetarget SNIR and generates transmit power control (TPC) commands toincrease (or decrease) the transmit power if the received SNIR is lessthan (or greater than) the target SNIR. In response to receiving the TCPcommands, the base station may adjust the transmit power of the downlinkDPCH.

In the W-CDMA system, for any given transport channel, the base stationcan specify to the terminal a particular target BLER. For dataintegrity, the actual BLER should not exceed the target BLER. At thesame time, the actual BLER should not consistently fall below the targetBLER, since that would imply excess transmit power is used for the datatransmission, which would then reduce the capacity of the transmittingbase station and may further cause unnecessary interference toneighboring cells.

The terminal and base station attempt to achieve and maintain the targetBLER specified for the transport channel through the power controlmechanism described above. For a transport channel with only onetransport format (i.e., transport blocks of equal sizes, whichtranslates into code blocks of uniform lengths), a steady statecondition in the power control is reached when the outer and inner loopsconverge on the target SNIR required (under the given channelconditions) to provide the target BLER for the (one) transport formatused for the transport channel. A power control mechanism that maintainsone individual outer loop for each transport channel is described inU.S. Pat. No. 6,748,234, entitled “METHOD AND APPARATUS FOR POWERCONTROL IN A WIRELESS COMMUNICATION SYSTEM,” issued Jun. 8, 2004,assigned to the assignee of the present application and incorporatedherein by reference.

However, in W-CDMA, data may be transmitted on a given transport channelusing many possible transport formats. For example, on a transportchannel for a voice call, shorter transport blocks may be sent whenthere is no voice activity and longer transport blocks may be sent whenthere is voice activity. The SNIR required to achieve the target BLERmay be very different for code blocks of different lengths, and thus therequired SNIRs may be different for different transport formats.

The W-CDMA standard currently allows one target BLER to be specified foreach transport channel regardless of the number of transport formatsthat may be used for this transport channel. Since different transportformats may require different target SNIRs to meet the target BLER asdescribed above, this W-CDMA specification is not precise. The averagetransmit power will likely fluctuate depending on the relative frequencyand/or order of succession of the transport formats used for thetransport channel.

If the outer loop converges on the target SNIR for a particulartransport format, and if the transport format is then changed, atransient time is typically required for the outer loop to convergeagain to the new target SNIR for the new transport format. During thistransient time, the actual BLER may be much greater or less than thetarget BLER. For a data transmission that uses a mix of transportformats, the duty cycle as well as the period of the duty cycle of thetransport formats may determine different values for the required targetSNIRs. For example, the outer loop will likely converge on differentsets of required SNIRs for the case of 10 TTIs of transport format 1,TF(1), alternating with 10 TTIs of TF(2), versus 20 TTIs of TF(1)alternating with 10 TTIs of TF(2), and so on. It is likely that thetarget BLER will not be met with the most efficient transmit power, ifat all, for all transport formats if a conventional power controlmechanism is used.

Moreover, when many transport formats are used for a given transportchannel, the target BLER may not need to be the same for all transportformats. For example, for a voice call, transport formats known to haveinsignificant voice content (e.g., background noise) may be able totolerate higher BLERs than transport formats with voice content.

Aspects of the invention provide various techniques to more effectivelyand efficiently control the transmit power for a data transmission thatuses a number of transport formats. The invention recognizes thatdifferent transport formats for a given transport channel may requiredifferent target SNIRs to achieve a particular BLER. Various schemes areprovided herein to effectively treat these different transport formatsas “individual” transmissions with their own performance requirementswhile reducing the overall transmit power for the data transmission.

In one aspect of the invention, a particular target BLER may bespecified for each transport format of each transport channel used for adata transmission, instead of a single target BLER for all transportformats of each transport channel. If N transport formats are availablefor use for a given transport channel, then up to N target BLERs may bespecified for the transport channel.

For each transport format TF(i) of a particular transport channelTrCH(k), SNIR_(TCk,TFi) is the SNIR required for a received BLER ofBLER_(TCk,TFi), which is the target BLER for the transport format. If Ntransport formats are available for use, then target SNIR_(TCk,TF1)through SNIR_(TCk,TFN) are required to respectively achieve targetBLER_(TCk,TF1) through BLER_(TCk,TFN) for transport formats TF(1)through TF(N). The power control mechanism can then be operated suchthat the proper set of target BLER and SNIR is used for each receivedtransport format, and to provide the proper power control commands basedon this set of target BLER and SNIR. Some power control mechanismscapable of achieving this are described in further detail below.

Specifying multiple individual target BLERs for each transport channelis more efficient since different types of data may have differentperformance requirements. Certain data may be more critical and wouldrequire a lower target BLER. Conversely, certain other data may be lesscritical and can tolerate a higher target BLER. At the extreme, a “don'tcare” target BLER may be specified for any transport format for whichthe BLER does not matter, in which case the power control mechanism maybe temporarily de-activated when these transport formats are used. The“don't care” target BLER may be explicitly specified (e.g., sent overthe air) or implicitly specified (e.g., by not specifying any value),and may be used, for example, for NULL/DTX transport blocks.

Multiple individual target BLERs for each transport channel allow for aspecification of the target BLER that is both efficient and independentof the selected transport format combination, their relative frequencyof occurrence, and their order of succession. The current W-CDMAstandard may be amended to support the specification of multiple targetBLERs for multiple transport formats for each transport channel.

In another aspect of the invention, various power control schemes areprovided to achieve different target SNIRs for different transportformats. These schemes may be used to achieve different target BLERsspecified for different transport formats, which generally requiredifferent target SNIRs. These schemes may also be used even if a singletarget BLER is specified for all transport formats of a given transportchannel, as in the current W-CDMA standard, since different transportformats may require different target SNIRs to achieve the same targetBLER. Some of these power control schemes are described below, andothers may also be implemented and are within the scope of theinvention.

In a first power control scheme for achieving different target SNIRs fordifferent transport formats, multiple individual outer loops aremaintained for multiple transport formats. For each transport format,its associated outer loop attempts to set the target SNIR such that thetarget BLER specified for that transport format is achieved. Themultiple individual outer loops would then form an overall outer loopthat operates in conjunction with the (common) inner loop to derive theproper power control commands for all transport formats. Variousembodiments of this power control scheme can be designed, some of whichare described below.

FIG. 6 illustrates a specific embodiment of the first power controlscheme whereby multiple individual outer loops are maintained to controlthe transmit power of a data transmission that uses multiple transportformats. In FIG. 6, the horizontal axis denotes time, which is providedin units of TTI. The vertical axis denotes the SNIR target that is usedby the inner loop power control at the terminal.

Prior to time t_(n), a number of DTX frames have been sent by the basestation with the data portion transmitted at a power level of Δ over thepower level of a “reference” portion of the frame (e.g., the pilotportion of the DPCCH shown in FIG. 4). This power offset Δ is typicallynot known to the terminal. The inner and outer loops typically operateon the reference portion of the frame, and the transmit power of thedata portion is adjusted by controlling the transmit power of thereference portion (i.e., the transmit power levels of the data andreference portions are ganged by Δ). The outer loop has settled on thetarget SNIR_(DTX) required on the data portion to achieve the targetBLER_(DTX) for DTX frames. The corresponding target SNIR for thereference portion, SNIR_(ref), provided by the outer loop to the innerloop for TTI(n) is thus SNIR_(ref)(n)=SNIR_(DTX)−Δ.

At time t_(n), the base station switches to a new transport format, anda full rate (FR) frame is transmitted during TTI(n), with the dataportion of the frame again being transmitted at a power level of Δ overthe reference portion of the frame. During the entire TTI(n), theterminal uses the reference portion target SNIR_(ref)(n) for the innerloop. This reference portion target SNIR_(ref)(n) was derived by theouter loop from the received frame in TTI(n−1), which was of frame typeDTX, since it has not determined that the transport format in TTI(n) haschanged. For W-CDMA, 15 power control commands are sent for each 10 msecframe, and each TTI may have a duration of 1, 2, 4, or 8 frames.

In the specific embodiment shown in FIG. 6, the terminal is not providedwith the transport format information a priori, and detects thetransport format only after the entire FR frame has been received andprocessed. In accordance with W-CDMA, the TFCI is sent every 10 msec,and the terminal may thus be able to detect the transport format afterreceiving the first 10 msec of the frame (e.g., after the first half ofa 20-msec AMR (FR, SID, or DTX) frame). If the transport format can bedetected before an entire frame is received (e.g., after only half of aDTX/SID/FR frame), then only a portion of the frame may be received atthe wrong target SNIR and the remaining portion of the frame may bereceived at the proper target SNIR. For simplicity, various aspects andembodiments of the invention are described for the case wherein theentire frame needs to be received before the transport format can beascertained. However, the techniques described herein may also beapplied in cases where the transport format can be determined prior toreceiving the entire frame (e.g., by decoding the TFCI right after thefirst 10 msec.

For the embodiment shown in FIG. 6, the SNIR on the reference portion ofTTI(n) will be driven to SNIR_(ref)(n+1)=SNIR_(DTX)−Δ, and the dataportion will be at SNIR_(DTX). This SNIR is less than the requiredSNIR_(FR) on the data portion of the FR frame to achieve BLER_(FR). Thefirst FR frame during TTI(n) will thus likely be received in errorbecause of the low received SNIR (i.e., for the FR frame) achieved usingthe target SNIR_(DTX) during TTI(n).

Shortly after time t_(n+1), the terminal determines that the FRtransport format was used for TTI(n), and accordingly updates thereference portion target SNIR_(ref)(n+1) for the inner loop from the oldtarget (SNIR_(DTX)−Δ) to the new target (SNIR_(FR)−Δ). This referenceportion target SNIR_(ref)(n+1) is then used for the inner loop duringthe reception of the frame in TTI(n+1). The terminal also updates thetarget SNIR_(FR) for FR frames based on the status of the received FRframe (e.g., good or erased) to achieve the target BLER_(FR) for FRframes. During TTI(n+1), another FR frame is transmitted and theterminal (correctly) uses the reference portion target SNIR_(ref)(n+1)for the inner loop.

At time t_(n+2), the base station switches to a new transport format,and a SID frame is transmitted during TTI(n+2) at a power level of Δover the reference power level. During the entire TTI(n+2), the terminaluses the reference portion target SNIR_(ref)(n+2)=SNIR_(FR)−Δ for thereference portion of the SID frames for the inner loop since it has notdetermined that the transport format in TTI(n+2) has changed. Shortlyafter time t_(n+3), the terminal determines that the transport formatfor the previous TTI(n+2) has changed, and switches to the outer loopfor SID frames. The reference portion targetSNIR_(ref)(n+3)=SNIR_(SID)−Δ is then used to drive the inner loop fromthis point forward, until another outer loop is selected. The terminalalso updates the target SNIR_(SID) for SID frames based on the status ofthe received SID frame to achieve the target BLER_(SID) for SID frames.

At time t_(n+3), the base station switches to the DTX transport format,and a DTX frame is transmitted during TTI(n+3). During the entireTTI(n+3), the terminal uses the reference portion targetSNIR_(ref)(n+3)=SNIR_(SID)−Δ for the inner loop since it has notdetermined that the transport format in TTI(n+3) has changed. Shortlyafter time t_(n+4), the terminal determines that the transport formatfor the previous TTI(n+3) has changed, and switches to the outer loopfor DTX frames. The reference portion targetSNIR_(ref)(n+4)=SNIR_(DTX)−Δ is then used to drive the inner loop fromthis point forward, until another outer loop is selected. The terminalalso updates the target SNIR_(DTX) for DTX frames based on the status ofthe received DTX frame to achieve the target BLER_(DTX).

In the first embodiment of the first power control scheme, as shown inFIG. 6, the transport format for the current TTI is not known a priori,and the terminal uses the target SNIR for the transport format receivedin the immediately prior TTI for the inner loop.

If the terminal is provided with information indicative of the specifictransport format being used for the current TTI before having to receivethe whole frame, then it can apply the proper outer loop and use theproper target SNIR for the inner loop during the TTI. This transportformat information may be provided to the terminal via variousmechanisms such as, for example, a predetermined schedule, a preamble atthe start of each transmitted frame, signaling on another transportchannel, and so on.

If the terminal is not provided with the transport format information apriori, then some delays exist in this power control scheme. The amountof delay is determined by the amount of time required to process areceived frame to ascertain the transport format used for the receivedframe. If an entire transmitted frame needs to be received and processedbefore the transport format can be ascertained, then a one-frame delay(or possibly more) exists between the time a new transport format isused for data transmission at the base station and the time the propertarget SNIR is used for power control at the terminal.

To reduce adverse effects due to delays caused by late detection of thetransport format, the transport format for the current TTI may bepredicted. This prediction may be made based on any available knowledgefor the data transmission. In this case, the target SNIR of thepredicted transport format (and not the maximum target SNIR) may be usedfor the inner loop, which may improve efficiency and performance.

In a second embodiment of the first power control scheme, to ensure thatsufficient transmit power is used at any given time for all transportformats that may be used in a particular TTI (i.e., “possible” transportformats), the target SNIR for all possible transport formats arecompared, and the maximum target SNIR is selected for use. If only asubset of all available transport formats may be used in a particularTTI, then the maximum can be taken over the subset of possible transportformats and not the total set of all available transport formats.

As noted above, if a delay exists in the power control mechanism due to“late” detection of the transport format, then an inappropriate targetSNIR may be used during the delay period when the transport format isnot known. The second embodiment thus ensures that sufficient transmitpower will be used regardless of the transport format selected. One ormore of the target SNIRs may be updated at the end of each TTI based onthe status of the received transport blocks, the transport format usedfor the TTI, and so on, as described below.

FIG. 7 is a flow diagram of an embodiment of a process 700 performed atthe terminal to maintain a number of individual outer power controlloops for a number of transport formats. Initially, the outer looptargets, SNIR_(TCk,TFi)(n), for all transport channels and all transportformats are set to some particular (e.g., arbitrary) initial value. Thecorresponding overall target SNIR, SNIR_(ref)(n), is also set at thesame value. The terminal receives data for K transport channels (i.e.,TrCH(k) where k=1, 2, . . . K, and K can be any integer one or greater)during TTI(n), at step 712. Each of the K transport channels is thenprocessed, one at a time starting with the first transport channel bysetting k=1, at step 714.

For transport channel TrCH(k), all transport formats (i.e., TF(i), wherei=1, 2, . . . N_(k), and N_(k) can be any integer one or greater)available for use for the transport channel are initially determined, atstep 716. A determination is then made whether any transport block intransport channel TrCH(k) was received in error for TTI(n), at step 718.This can be achieved, for example, by performing the CRC parity check oneach received transport block.

In an embodiment, if any transport block in transport channel TrCH(k)was received in error in TTI(n), then the entire transmission fortransport channel TrCH(k) during the TTI is deemed to have beentransmitted with insufficient transmit power. Thus, if any transportblock in transport channel TrCH(k) in TTI(n) was received in error, asdetermined in block 720, then the target SNIR, SNIR_(TCk,TFi), for eachtransport format actually used in TTI(n) is increased by that transportformat's upward adjustment, ΔUP_(TCk,TFi), at step 722. The transportformats actually used in TTI(n) can be ascertained based on the TFCIsent on the downlink DPCH or by “blind detection” (e.g., as described inDocument No. 3GPP TS 25.212, which is incorporated herein by reference).The upward adjustment of the target SNIR for each transport format inTTI(n) can be achieve as follows:SNIR_(TCk,TFi)(n+1)=SNIR_(TCk,TFi)(n)+ΔUP_(TCk,TFi)(dB).  Eq (1)Step 722 is performed for all transport channels used in TTI(n). (Allavailable transport channels are assumed to be used in each TTI. Ifnothing was sent on a transport channel, then the transport format forthat transport channel is {0 block size, 0 blocks}.)

In an embodiment, if all transport blocks in transport channel TrCH(k)in TTI(n) were received correctly with transport format TF(i), and iftransport format TF(i) has a target SINR equal to SNIR_(ref)(n), thenits SNIR target, SNIR_(TCk,TFi)(n), is decreased by the down step sizeΔDN_(TCk,TFi). The target SNIRs of the other transport channels are notreduced since they are lower than SNIR_(ref)(n) and were not selectedfor use by the inner loop. In general, the target SNIR adjustmentperformed at the terminal should be complementary to the specific schemeused to select the target SNIR for the inner loop.

For each transport format TF(i) actually used in TTI(n), a determinationis then made whether or not that transport format's target SNIR,SNIR_(TCk,TFi)(n) is equal to SNIR_(ref)(n), at step 734. If the answeris yes, then that transport format's target SNIR is adjusted downward,at step 738, as follows:SNIR_(TCk,TFi)(n+1)=SNIR_(TCk,TFi)(n)−ΔDN_(TCk,TFi)(dB).  Eq (2)Otherwise, if the transport format's target SNIR is not equal toSNIR_(ref)(n), then its current value is maintained, at step 736. Step734 and either step 736 or 738 are performed for each transport formatactually used in TTI(n).

After all applicable transport formats for transport channel TrCH(k)have been updated (in steps 722, 736, and 738), a determination is madewhether or not all K transport channels have been processed, at step740. If the answer is no, then the next transport channel is consideredfor processing by incrementing k, in step 742, and returning to step716. Otherwise, if all K transport channels have been processed, thenthe reference portion target SNIR_(ref)(n+1) for the next TTI(n+1) isdetermined, at step 744. For the first embodiment of the first powercontrol scheme, as described in FIG. 6, the reference portion targetSNIR_(ref)(n+1) can be determined as the maximum target SNIR for alltransport formats actually used in TTI(n). And for the second embodimentof the first power control scheme, the reference portion targetSNIR_(ref)(n+1) can be determined as the maximum target SNIR for alltransport formats available for use for all K transport channels. Thisreference portion target SNIR_(ref)(n+1) is then provided to the innerloop. The processing is then repeated for the next TTI(n+1) byincrementing n, at step 746

The first power control scheme described above may be applied when theTTIs of all transport channels multiplexed together on the same downlinkDPCH are the same. When the TTIs of the transport channels are differentfrom one another, then the outer loop may be modified as follows. TheTTI index n would no longer be incremented per TTI, but per 10 msecframe. The target SNIR_(TCk,TFi) for TF(i) of TrCH(k) would only beupdated if frame n corresponded to the last frame in the TTI of TrCH(k).This is because the entire TTI of a transport channel needs to bereceived to determine whether a block error has occurred in one of thetransport blocks. Also, the determination of whether or not the targetSNIR is equal to the target SNIR_(ref) is performed for each 10 msecframe, and the target SNIR can go down as long as during any one 10 msecframe the transport format is the one that limits the outer loop.

In a second power control scheme for achieving different target SNIRsfor different transport formats, multiple individual outer loops aremaintained for multiple transport formats, and the base station furtherapplies different adjustments to the transmit power levels for differenttransport formats. As noted above, if there is a delay in the powercontrol mechanism, then the maximum target SNIR for all availabletransport formats may be used for the inner loop to ensure that theproper transmit power is used for the data transmission. The use of themaximum target SNIR for the inner loop, since the specific transportformat(s) to be used is not known, may unnecessarily waste power ifthere is a big difference between the maximum SNIR and the SNIR of thetransmitted transport format. However, since the base station hasknowledge of the specific transport format(s) that will be used for theupcoming TTI, it can also participate in the power control by adjustingits transmit power for the data transmission based on the actualtransport format combination selected for use, ideally making alltransport formats require the same reference SNIR.

In one embodiment, the base station is provided with a table of therelative difference in the target SNIR required for each transportformat to achieve the target BLER. For each TTI, the base stationselects one or more transport formats for use for the TTI, retrievesfrom the table the relative target SNIR difference for each selectedtransport format, and transmits at the power level determined in part bythe relative target SNIR difference(s) for the selected transportformat(s).

As a specific example, a particular target BLER (e.g., 1%) may berequired for the FR, SID, and DTX transport formats. This may require FRframes to be transmitted at +2.5 dB over a particular reference powerlevel, SID frames to be transmitted at +2.0 dB over the reference powerlevel, and DTX frames to be transmitted at +0.8 dB over the referencepower level. The base station may transmit a long string of DTX framesat +0.8 dB over the reference power level, and suddenly switches to theSID transport format. The base station would then automatically adjustthe transmit power for this SID frame from +0.8 dB to +2 dB over thereference power level, as derived from its look-up table, withoutwaiting for the terminal to tell it to do so via power control.

For this second power control scheme, if the terminal's inner loop isdriven off of the data portion of the receive frame, or if the basestation applies the power offset described above to the entire frame(i.e., the data and reference portions), then the terminal may assumethat the channel conditions have changed and may try to reverse the(transport format dependent) power adjustment made by the base station.This counter action occurs because the terminal's inner loop detectsthat the received power has suddenly changed without it having sent anycorresponding power control commands. Moreover, this counter action bythe terminal would only occur if the terminal needs to process an entirereceived frame in order to ascertain the transport format for thatreceived frame and, until then, would not be aware that the change inreceived power level was due to a new transport format, and not changesin channel conditions. Therefore, the base station may apply the poweroffset described above only to the data portion of the frame, and theterminal's inner loop may be driven off of only the reference portion ofthe receive frame. If only the transmit power of the data portion isadjusted based on transport format, then the terminal's inner loop wouldnot detect any change in the received power in the reference portion.

As described above, the base station's (transport format dependent)power adjustment may be made only to the data portion of the transmittedframe while maintaining (i.e., do not adjust based on transport format)the transmit power level for the remaining portion of the transmittedframe that is used by the terminal to perform inner loop power control.Referring back to FIG. 4, for the downlink transmission in the W-CDMAsystem, the power adjustment may be applied by the base station to onlythe DPDCH (which carries the data portion), while the power level forthe DPCCH (which carries the control or reference portion of the frame)may be maintained and not made dependent on transport format.

The transmit power for the DPDCH may thus be varied from the transmitpower for the DPCCH based on a “power offset” that is dependent ontransport format. The transmit power for the DPCCH (and thus the DPDCH)would be adjusted in the normal manner based on the power controlcommands derived from the inner loop.

As shown in FIG. 4, the DPCCH includes the pilot, TFCI, and TPC fields.If only the pilot is used for power control by the inner loop and sincethe DPCCH is not adjusted based on transport format, then the terminalwould not try to power down a sudden change in the power level for theDPDCH. The transmit power for the DPCCH is thus used as the referencepower level, and the transmit power for the DPDCH may be adjustedrelative to the reference power level for the DPCCH depending on thespecific transport format(s) used for the DPDCH. At the terminal, theinner loop can be operated to keep the DPCCH at the (reference portion)target SNIR supplied by the overall outer loop, as described below.

Once the terminal ascertains the current transport format as TF(i), thecorresponding target SNIR is adjusted by the outer loop, and the targetSNIR for that transport format (and possibly other transport formats) isused to derive the reference portion target SNIR that is then used todrive the inner loop for the next TTI. This then reduces (or possiblyeliminates) the time and excess transmit power needed for the outer loopto re-converge on the reference portion target SNIR when the transportformat is changed.

FIG. 8 illustrates an embodiment of a second power control scheme withmultiple individual outer loops and transport format dependent poweradjustment at the base station. It is assumed that the base station hasknowledge of the target SNIR_(FR), SNIR_(SID), and SNIR_(DTX) requiredfor the terminal to achieve the target BLER_(FR), BLER_(SID), andBLER_(DTX), respectively. These values of SNIR_(FR), SNIR_(SID), andSNIR_(DTX) are, in general, channel-dependent and may further changeover time. The techniques described herein thus apply for time-varianttarget SNIRs. For simplicity, the constant values are used for thetarget SNIR_(FR), SNIR_(SID), and SNIR_(DTX). Techniques to derive andprovide these target SNIRs are described in further detail below.

Prior to time t_(n), a number of DTX frames have been sent by the basestation with the data portions transmitted at an adjusted power levelthat is Δ_(DTX) over the power level of the reference portion of theframe. The outer loop has settled on the target SNIR_(DTX) required onthe data portion to achieve the target BLER_(DTX) for DTX frames. Sincethe inner loop typically operates on the reference portion of the frame,the target SNIR_(ref) provided by the overall outer loop for thereference portion of the frame isSNIR_(ref)=SNIR_(DTX,ref)=SNIR_(DTX)−Δ_(DTX), and this target SNIR_(ref)is used to drive the inner loop.

At time t_(n), the base station switches to a new transport format, anda FR frame is transmitted during TTI(n), with the data portion of theframe being transmitted at an adjusted power level that is Δ_(FR) overthe reference portion of the frame. During the entire TTI(n), theterminal uses the reference portion target SNIR_(ref) derived fromTTI(n−1) for the inner loop, which was of frame type DTX. Thus, the SNIRon the reference portion of TTI(n) will be driven toSNIR_(DTX,ref)=SNIR_(DTX)−Δ_(DTX)+ΔUP or ΔDN, and the SNIR for the dataportion will be at SNIR_(DTX)−Δ_(DTX)+Δ_(FR)+ΔUP or ΔDN. This dataportion SNIR may or may not be equal to the required SNIR_(FR) on thedata portion to achieve BLER_(FR). However, since it is assumed that thebase station has accurate knowledge of SNIR_(FR) and SNIR_(DTX)(specifically, their difference), the base station can set thedifference (Δ_(FR)−Δ_(DTX)) to be precisely (SNIR_(FR)−SNIR_(DTX)). Inthat case, the data portion of TTI(n) would be driven to SNIR_(FR),since SNIR_(DTX)−Δ_(DTX)+Δ_(FR)=SNIR_(FR) whenΔ_(FR)−Δ_(DTX)=SNIR_(FR)−SNIR_(DTX).

Shortly after time t_(n+1), the terminal determines that the FRtransport format was used for TTI(n), and accordingly updates the innerloop target (SNIR_(DTX)−Δ_(DTX)) to the new target (SNIR_(FR)−Δ_(FR))for use during the reception of TTI(n+11), based on the status of thereceived FR frame (e.g., good or erased) to achieve the targetBLER_(FR). During TTI(n+1), another FR frame is transmitted and theterminal continues to use the reference portion target SNIR_(ref). InFIG. 8, (SNIR_(DTX)−Δ_(DTX)) is shown as being at the same level as(SNIR_(FR)−Δ_(FR)), which results from the assumption that the basestation sets Δ_(FR)−Δ_(DTX)=SNIR_(FR)−SNIR_(DTX).

At time t_(n+2), the base station switches to a new transport format,and a SID frame is transmitted during TTI(n+2) at an adjusted powerlevel that is Δ_(SID) over the reference power level. Shortly after timet_(n+3) the terminal determines that the SID transport format was usedfor TTI(n+2) and accordingly updates the target SNIR_(SID) for SIDframes based on the status of the received SID frame to achieve thetarget BLER_(SID). The reference portion target SNIR_(ref) is thenupdated again.

At time t_(n+3), the base station switches to the DTX transport format,and a DTX frame is transmitted during TTI(n+3) at the adjusted powerlevel of Δ_(DTX) over the reference power level. Shortly after timet_(n+4), the terminal determines that the DTX transport format was usedfor TTI(n+3) and accordingly updates the target SNIR_(DTX) for DTXframes based on the status of the received DTX frame to achieve thetarget BLER_(DTX). The reference portion target SNIR_(ref) is thenupdated.

FIG. 9 is a diagram illustrating a specific implementation of the secondpower control scheme. At base station 104, a table 910 is maintainedthat lists all transport channels used for a data transmission toterminal 106 and all transport formats available for use for eachtransport channel. For each transport format, table 910 also lists aspecific power offset, Δ_(TCk,TFi), to be applied to the data portion(e.g., the DPDCH) if that transport format is selected for use.

In W-CDMA, one or more transport channels may be multiplexed onto acoded composite transport channel (CCTrCH) that is then transmittedusing a single power control mechanism. To ensure that the propertransmit power level is used for the transmitted transport formats onall transport channels multiplexed in the data transmission, a poweroffset may be maintained for each transport format of each transportchannel. For any given TTI, the maximum of the power offsets for alltransport formats selected for use for that TTI is determined, and thismaximum power offset may be used for power adjustment for the datatransmission for that TTI. This then ensures that each transport formatin the TTI will be transmitted with sufficient power to maintain itsspecified target BLER.

For each TTI, the base station determines a set of quantities used toadjust the transmit power for the data transmission (step 912). Thesequantities include, for example:

-   -   1) the power offset to be used for the transport format selected        for use in a particular TTI for each transport channel (e.g.,        power offsets Δ_(TCA) and Δ_(TCB) for transport channels A and        B, respectively, for the example shown in FIG. 9),    -   2) the maximum power offset for all transport channels (e.g.,        Δ_(max)=max {Δ_(TCA), Δ_(TCB)}), and    -   3) the transmit power to be used for the DPDCH based on the        transmit power for the DPCCH and the maximum power offset (i.e.,        P_(DPDCH)=P_(DPCCH)+Δ_(max)).        The transmit power for the DPCCH is adjusted based on the power        control commands received from the terminal, which are generated        by the inner loop. The DPCCH for this TTI is then transmitted at        the transmit power P_(DPCCH), and the DPDCH for this TTI is        transmitted at the transmit power P_(DPDCH) (step 914).

At terminal 106, a table 930 is maintained that lists all transportchannels used for the data transmission, the available transport formatsfor each transport channel, and the target SNIR for the referenceportion of the frame for each transport format. Each reference portiontarget SNIR in table 930 is associated with a respective individualouter loop maintained by the terminal for the corresponding transportformat. The overall outer loop may be viewed as being comprised of theindividual outer loops for all transport formats. The reference portiontarget SNIRs listed in table 930 are to be used to derive the inner loopsetpoint for the reference portion (e.g., the DPCCH) of the receiveframe.

For each TTI, the transport format for each transport channel used forthe received frame is ascertained, and the status of each receivedtransport block is also determined (e.g., good or erased). For eachtransport format actually used during the TTI(n), the reference portiontarget SNIR_(TCk,TFi,ref) for the transport format is updated (i.e.,adjusted either up or down, or maintained at the current level) based ona particular outer loop power control scheme, which may take intoaccount whether or not a block error was previously received and/or theactual transmit power used on the data portion during the last TTI.

The overall outer loop provides a single reference portion target SNIRto the inner loop, SNIR_(ref), and this reference portion target SNIRmay be updated in each frame, since the transport channels multiplexedtogether may have different TTIs. For each frame, after the transportformats for all transport channels used in the current frame have beenascertained, the individual outer loops perform the necessaryadjustments for those transport channels that have just finishedreceiving a full TTI in the last frame, and the target SNIR for theDPCCH is updated accordingly. Table 930 lists the possible referenceportion target SNIRs for the DPCCH. For each transport format of eachtransport channel, the target SNIR for the reference portion of theframe, SNIR_(TCk,TFi,ref), is related to the target SNIR for the dataportion of the frame, SNIR_(TCk,TFi,data), as follows:SNIR_(TCk,TFi,ref)=SNIR_(TCk,TFi,data)−Δ_(TCk,TFi)(dB),  Eq (3)where Δ_(TCk,TFi) is the power offset used at the base station fortransport format TF(i) of transport channel TrCH(k).In actuality, the individual outer loops adjust the targetSNIR_(TCk,TFi,ref) for the reference portion of the frames to achievethe target BLER for the data portion, and thus the targetSNIR_(TCk,TFi,data) for the data portion is achieved indirectly.

Since the transport formats for the upcoming TTI are not known a priori,the target SNIR to be used by the inner loop for the DPCCH may beselected as the maximum of all reference portion target SNIRs for allavailable transport formats (if no information is available as to theparticular transport formats to be used in the upcoming TTI). For theexample shown in FIG. 9, the reference portion target SNIR for the innerloop, SNIR_(ref), may be computed as:SNIR_(ref)=max{SNIR_(TCA,TF1,ref), SNIR_(TCA,TF2,ref),SNIR_(TCA,TF3,ref), SNIR_(TCB,TF1,ref)}.  Eq (4)If the transport format for any portion of a TTI is known (e.g., afterdecoding the first 10 msec frame), then the reference portion targetSNIR for that transport format may be used as SNIR_(ref) for thesubsequent portion of the TTI. The SNIR_(ref) is used for the inner loopto derive the power control commands, which are then provided to thebase station (step 934). The base station may then adjust the transmitpower for the DPCCH (up or down) based on the received power controlcommands. The transmit power for the DPDCH is also adjustedcorrespondingly, since it is “ganged” to the transmit power for theDPCCH by the applied power offset, Δ_(max).

The power offsets used for different transport formats may be derivedand maintained in numerous ways. As described above, the goal is to setvalues for Δ_(TCk,TFi) and Δ_(TCk′,TFi′) (for two different transportchannels k and k′, with different transport formats i and i′) such that(Δ_(TCk,TFi)−Δ_(TCk′,TFi′)) is equal to(SNIR_(TCk,TFi)−SNIR_(TCk′,TFi′)) at the receiver. In one embodiment,fixed power offsets are used at the base station for the duration of thecommunication with the terminal. The values for the power offsets may bedetermined based on empirical measurements (in the lab or field),computer simulation, and so on. In another embodiment, the power offsetsare determined at the terminal and provided to the base station.

FIG. 10 is a diagram illustrating a specific embodiment of the thirdpower control loop to derive the power offsets for multiple transportformats used for a data transmission. In this embodiment, the terminalmaintains an individual outer loop for each transport format, and theoverall outer loop is comprised of these individual outer loops, asdescribed above. The terminal also assists in the determination of therelative differences between the reference portion target SNIRs forthese transport formats and a base SNIR, which may be selected as thereference portion target SNIR for one of the transport formats. Theserelative differences comprise the updates to the power offsets, and areprovided from the terminal to the base station. The power offset updatesmay be sent periodically, or only when it is determined that the channelconditions have changed sufficiently to warrant a transmission.

At base station 104, table 910 is maintained that lists all transportchannels used for data transmission, the transport formats available foruse for each transport format, and the power offset for each transportformat. For each frame, the base station determines the transmit powerfor the DPCCH, P_(DPCCH), and further computes the transmit power to beused for the DPDCH, P_(DPDCH), based on the DPCCH transmit power, thetransport formats to be used for the TTI, and the power offsetsassociated with these transport formats (step 912). The base stationthen transmits the DPCCH at the transmit power P_(DPCCH), and DPDCH atthe transmit power P_(DPDCH) (step 914). Steps 912 and 914 are asdescribed above.

At terminal 106, the transmitted frames are received and used to adjustthe reference portion target SNIRs for the various transport formats, asdescribed above. Updates to the power offsets may also be derived basedon the reference portion target SNIRs for the transport formats and thebase SNIR, which may be the reference portion target SNIR for one of thetransport formats (step 942). The updated power offset, δ_(TCk,TFi), foreach transport format may be computed as:δ_(TCk,TFi)=SNIR_(TCk,TFi,ref)−SNIR_(base (dB).)  Eq (5)For the example shown in FIG. 10, the base SNIR is selected asSNIR_(TCA,TF1,ref), and the power offset updates, δ_(TCk,TFi), may thenbe computed as:δ_(TCA,TF1)=SNIR_(TCA,TF1,ref)−SNIR_(TCA,TF1,ref),δ_(TCA,TF2)=SNIR_(TCA,TF2,ref)−SNIR_(TCA,TF1,ref),δ_(TCA,TF3)=SNIR_(TCA,TF3,ref)−SNIR_(TCA,TF1,ref), andδ_(TCB,TF1)=SNIR_(TCB,TF1,ref)−SNIR_(TCA,TF1,ref).The power offset updates attempt to minimize the difference between thereference portion target SNIRs for all transport formats such that theyare all approximately equal. In this way, the changes in the referenceportion target SNIRs applied to inner loop are small regardless of thetransport formats selected for use.

Although not shown in equation (5), the power offset updates for eachtransport format may be filtered based on a particular (e.g., lowpass)filter response to obtain an averaged value. In general, the timeconstant of the filter used for the power offset should be longer thanthe time constant for the outer loop.

The power offset updates may be provided from the terminal to the basestation based on various update schemes (step 944). In a first updatescheme, all power offset updates are provided to the base stationperiodically at a predetermined time interval, t_(update). In a secondupdate scheme, the power offset updates for each transport channel areprovided to the base station periodically (e.g., at predetermined timesselected for that transport channel) and/or as necessary. For thisscheme, the power offset updates for different transport channels may beprovided to the base station at different times and/or different timeintervals, t_(TCk,update). In a third update scheme, the power offsetupdates for each transport format are provided to the base stationperiodically (e.g., at predetermined times selected for that transportformat) and/or as necessary. Again, the power offset updates fordifferent transport formats may be provided to the base station atdifferent times and/or different time intervals, t_(TCk,TFi,update).

In a fourth update scheme, the power offset updates are provided to thebase station when certain condition is satisfied. For example, the poweroffset updates may be provided if the maximum power offset updateexceeds a particular threshold, Th. For the example shown in FIG. 10,this can be expressed as:max{|δ_(TCA,TF1)|, |δ_(TCA,TF2)|, |δ_(TCA,TF3)|, |δ_(TCB,TF1)|}>Th.

In a fifth update scheme, the power offset updates for each transportformat are provided to the base station when certain condition issatisfied, e.g., if the power offset updates for the transport formatexceed a threshold, Th_(TFi), that is specific to that transport format.This can be expressed as:|δ_(TCk,TFi)|>Th_(TFi).Various other update schemes may also be implemented and are within thescope of the invention.

The base station receives the power offset updates from the terminal andupdates its table of power offsets. The power offset for each transportformat of each transport channel may be updated as follows:Δ_(TCk,TFi)(n+1)=Δ_(TCk,TFi)(n)+δ_(TCk,TFi)(n).  Eq (6)The base station then uses the updated power offsets to adjust thetransmit power of the DPDCH, as described above.

Correspondingly, for each transport format of each transport channelactually used during a given TTI, the terminal may update the referenceportion target SNIR, SNIR_(TCk,TFi,ref), for that transport format. Theterminal further derives the reference portion target SNIR_(ref) for theinner loop based on updated reference portion target SNIRs, which may becomputed as shown in equation (4) based on the reference portion targetSNIR for one or more transport formats (e.g., all available transportformats, only the transport formats used in the previous TTI, or someother set of transport formats).

Referring back to FIG. 5, the third loop 530 may be implemented betweenthe terminal and base station. At the terminal, the base SNIR and thereference portion target SNIRs, SNIR_(TCk,TFi,ref), for the transportformats are used to derive updates for the power offsets (block 526).Additional processing (e.g., filtering) may also be performed on thepower offset updates in block 526. The power offset updates are thenprovided to the base station based on a particular update scheme andused by the base station to perform the transport format dependent poweradjustment (block 516).

FIG. 11 is a flow diagram of an embodiment of a process 1100 performedat the terminal to maintain a number of individual outer loops for anumber of transport formats and using transport format dependent poweradjustment at the base station. Initially, the terminal receives datafor K transport channels (i.e., TrCH(k) where k=1, 2, . . . K) duringTTI(n), at step 1110. The terminal then determines the targetSNIR_(ref)(n) to be used on the reference portion during frame n, whichmay be determined with any available knowledge of the transport formatcombination of frame n at step 1112. Each of the K transport channels isthen processed, one at a time starting with the first transport channelby setting k=1, at step 1114.

For transport channel TrCH(k), all transport formats (i.e., TF(i), wherei=1, 2, . . . N) available for use for the transport channel areinitially determined, at step 1116. A determination is then made whetherany transport in block transport channel TrCH(k) was received in errorfor TTI(n), at step 1118. This can be achieved by performing the CRCparity check on each received transport block.

In an embodiment, if any transport block in transport channel TrCH(k) isreceived in error in TTI(n), then the entire transmission (i.e., alltransport formats) during the TTI is deemed to have been transmittedwith insufficient transmit power. Thus, if any transport block intransport channel TrCH(k) in TTI(n) was received in error, as determinedin block 1120, then the reference portion target SNIR,SNIR_(TCk,TFi,ref), for each transport format actually used duringTTI(n) is increased by that transport format's upward adjustment,ΔUP_(TCk,TFi), at step 1122. The upward adjustment of the target SNIRfor each transport format in TTI(n) can be achieve as follows:SNIR_(TCk,TFi,ref)(n+1)=SNIR_(TCk,TFi,ref)(n)+ΔUP_(TCk,TFi)(dB).  Eq (7)

In an embodiment, if all transport blocks in transport channel TrCH(k)in TTI(n) were received correctly, then only the reference portiontarget SNIR that was equal to the target SNIR_(ref)(n) of the receivedframe is adjusted downwards by ΔDN_(TCk,TFi). If the base stationdetermines the transmit power for the data transmission during TTI(n)based on the largest power offset for all transport formats actuallyused during the TTI, as described in FIG. 9, then only the largestreference portion target SNIR of all transport formats actually used forall transport channels in TTI(n) is reduced while the reference portiontarget SNIRs for all other transport formats are maintained at theircurrent levels. In general, the target SNIR adjustment performed at theterminal should be complementary to the transmit power adjustmentperformed at the base station.

Thus, if all transport blocks in transport channel TrCH(k) were receivedcorrectly in TTI(n), as determined in block 1120, then for eachtransport format actually used in TTI(n), a determination is then madewhether or not that transport format's reference power level,SNIR_(TCk,TFi,ref), is equal to SNIR_(ref)(n), at step 1134. If theanswer is yes, then that transport format's target SNIR is adjusteddownward, at step 1138, as follows:SNIR_(TCk,TFi,ref)(n+1)=SNIR_(TCk,TFi,ref)(n)−ΔDN_(TCk,TFi)(dB).  Eq (8)Otherwise, if the transport format's reference power level is not equalto SNIR_(ref)(n), then its current value is maintained, at step 1136.Step 1134 and either step 1136 or 1138 are performed for each transportformat actually used in during TTI(n).

After all applicable transport formats have been updated (in steps 1122,1136, and 1138), a determination is made whether or not all K transportchannels have been processed, at step 1140. If the answer is no, thenthe next transport channel is considered for processing by incrementingk, in step 1142, and returning to step 1116. Otherwise, if all Ktransport channels have been processed, then the maximum referenceportion target SNIR for all transport formats available for use for allK transport channels is then determined, in step 1144, and selected asthe reference portion target SNIR_(ref)(n+1) to be provided to the innerloop. The processing is then repeated for the next TTI(n+1) byincrementing n, at step 1146.

For the embodiment described in FIG. 11, the maximum of all transportformats possible on a transport channel is used to determineSNIR_(ref)(n+1). This is different from the embodiment shown in FIG. 8in which the radio frame carried only one transport channel, and onlythe current transport format received in frame n is used to determineSNIR_(ref)(n+1). These and other embodiments are within the scope of theinvention.

The (transport format dependent) power adjustment by the base stationbased on the power offsets for the transport formats selected for usemay also be implemented independently, i.e., without operating multipleindividual outer loops for the transport formats. The power adjustmentmay be made to the data portion (e.g., the DPDCH) of each transmittedframe and the reference portion (e.g., the DPCCH or the pilot) of thetransmitted frame may be maintained. A single (e.g., conventional) outerloop may be maintained to adjust the transmit power for the referenceportion, which would corresponding adjust the transmit power for thedata portion.

Another aspect of the invention provides a mechanism to more accuratelyreport the actual BLER. In an embodiment, the measured BLER used by theterminal to set the outer loop should be calculated as (the number ofreceived transport blocks that pass CRC, excluding zero-block transportformat) divided by (the total number of transport blocks received,excluding zero-block CRCs). This is also the BLER that may be reportedto the base station, if the base station asks for a measurement of theactual BLER. If the transport format combination indicator (TFCI) isreceived incorrectly, or if the blind transport format detection (BTFD)performed by the terminal is faulty, then the BLER may be calculatedincorrectly.

In some instances, the terminal is requested to report the measured BLERto the base station. Rather than have the terminal report to the basestation the BLER as calculated by the terminal, the terminal may reportto the base station just the number of frames (or data blocks) receivedcorrectly, and the base station may then determine the BLER itself.Since the base station knows which transport formats were used, it coulduse this knowledge to accurately calculate the BLER.

FIG. 12 is a block diagram of an embodiment of base station 104, whichis capable of implementing various aspects and embodiments of theinvention. On the downlink, data for a particular terminal anddesignated for transmission on one or more transport channels of thedownlink DPCH is received and processed (e.g., formatted, encoded) by atransmit (TX) data processor 1212. The processing for the downlink DPCHmay be as described above in FIG. 2A, and the processing (e.g.,encoding) for each transport channel may be different from that of theother transport channel. The processed data is then provided to amodulator (MOD) 1214 and further processed (e.g., channelized (orspread, in W-CDMA terminology) and further spread (or scrambled, inW-CDMA terminology)). The modulated data is then provided to an RF TXunit 1216 and conditioned (e.g., converted to one or more analogsignals, amplified, filtered, and quadrature modulated) to generate adownlink modulated signal. The downlink modulated signal is routedthrough a duplexer (D) 1222 and transmitted via an antenna 1224 to therecipient terminal.

FIG. 13 is a block diagram of an embodiment of terminal 106. Thedownlink modulated signal is received by an antenna 1312, routed througha duplexer 1314, and provided to an RF receiver unit 1322. RF receiverunit 1322 conditions (e.g., filters, amplifies, downconverts, anddigitizes) the received signal and provides samples. A demodulator 1324receives and processes (e.g., descrambles, channelizes, and pilotdemodulates) the samples to provide recovered symbols. Demodulator 1324may implement a rake receiver that processes multiple signal instancesin the received signal and generates combined recovered symbols. Areceive (RX) data processor 1326 then decodes the recovered symbols foreach transport channel, checks each received transport block, andprovides the output data and the decoding status of each receivedtransport block (e.g., good or erased). Demodulator 1324 and RX dataprocessor 1326 may be operated to process a data transmission receivedcan multiple transport channels and using multiple transport formats.The processing by demodulator 1324 and RX data processor 1326 may be asdescribed above in FIG. 2B.

For the downlink power control, the samples from RF receiver unit 1322may also be provided to an RX signal quality measurement unit 1328 thatestimates the received SNIR of the data transmission on the downlinkDPCH. The SNIR may be estimated based on the pilot included in the DPCCHand using various techniques, such as those described in U.S. Pat. Nos.6,097,972, 5,903,554, 5,056,109, and 5,265,119.

The received SNIR estimates for the downlink DPCH are provided to apower control processor 1330, which compares the received SNIR to thetarget SNIR, and generates the appropriate power control information(which may be in the form of TPC commands). The power controlinformation for the downlink DPCH is then sent back to the base station.

Power control processor 1330 also receives the status of the transportblocks (e.g., from RX data processor 1326) and one or more othermetrics. For example, power control processor 1330 may receive thetarget BLER, the ΔUP and ΔDN, and so on, for each transport format.Power control processor 1330 then updates the target SNIRs for thetransport formats based on the status of the received transport blocksand their target BLERs, and computes the reference portion targetSNIR_(ref) to be used for the inner loop for the upcoming TTI. Dependingon the particular power control scheme being implemented, power controlprocessor 1330 may further maintain a third power control loop thatderives the power offset updates to be used for the transport formats. Amemory 1332 may be used to store various types of power controlinformation such as the target SNIRs for the transport formats and thepower offset updates.

On the uplink, data is processed (e.g., formatted, encoded) by atransmit (TX) data processor 1342, further processed (e.g., channelized,scrambled) by a modulator (MOD) 1344, and conditioned (e.g., convertedto analog signals, amplified, filtered, and quadrature modulated) by anRF TX unit 1346 to generate an uplink modulated signal. The powercontrol information (e.g., TPC commands, power offset updates, and soon) from power control processor 1330 may be multiplexed with theprocessed data within modulator 1344. The uplink modulated signal isrouted through duplexer 1314 and transmitted via antenna 1312 to one ormore base stations 104.

Referring back to FIG. 12, at the base station, the uplink modulatedsignal is received by antenna 1224, routed through duplexer 1222, andprovided to an RF receiver unit 1228. RF receiver unit 1228 conditions(e.g., downconverts, filters, and amplifies) the received signal andprovides a conditioned signal for each terminal being received. Achannel processor 1230 receives and processes the conditioned signal forone terminal to recover the transmitted data and power controlinformation. A power control processor 1240 receives the power controlinformation (e.g., TPC commands, power offset updates, and so on, or acombination thereof) and adjusts the transmit power for the downlinkDPCH. Power control processor 1240 further updates the power offsets forthe transport formats based on the received power offset updates. Amemory 1242 may be used to store various types of power controlinformation such as the power offsets to be used for the varioustransport formats.

In FIGS. 12 and 13, power control processors 1240 and 1330 implementpart of the inner and outer loops (and possibly the third loop)described above. For the inner loop, power control processor 1330 isprovided with the estimated received SNR and sends back information(e.g., TPC commands) to the base station. Power control processor 1240at the base station receives the TPC commands and accordingly adjuststhe transmit power of the data transmissions on the downlink DPCH. Forthe outer loop, power control processor 1330 receives the transportblock status from RX data processor 1326 and adjusts the target SNIRsfor the proper transport formats.

The power control techniques described herein can be implemented byvarious means. For example, a power control mechanism can be implementedwith hardware, software, or a combination thereof. For a hardwareimplementation, the elements used for power control can be implementedwithin one or more application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), controllers,micro-controllers, microprocessors, other electronic units designed toperform the functions described herein, or a combination thereof.

For a software implementation, the elements used for power control canbe implemented with modules (e.g., procedures, functions, and so on)that perform the functions described herein. The software code can bestored in a memory unit (e.g., memories 1242 and 1332) and executed by aprocessor (e.g., power control processors 1240 and 1330). The memoryunit may be implemented within the processor or external to theprocessor, in which case it can be communicatively coupled to theprocessor via various means as it known in the art.

For clarity, various aspects, embodiments, and features of the powercontrol techniques have been described specifically for the downlinkpower control in W-CDMA. The techniques described herein may also beused for other communication systems (e.g., other CDMA-based systems, orpower-controlled systems) in which certain attributes (e.g., rates,transport formats, of formats) of a data transmission on a particular“logic channel” (e.g., a transport channel) can results in differentcharacteristics (e.g., different target SNIRs) for the power controlmechanism. The techniques described herein may thus be used for powercontrol of different attribute values (e.g., different rates, formats,or transport formats) of a data channel (e.g., transport channel)transmitted on a power-controlled physical channel (e.g., the downlinkDPCH). The techniques described herein may also be used for the uplinkpower control.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

1. A method for communication comprising: transmitting, to a receivingapparatus, a first frame in accordance with a first transport format andat a first power level corresponding to the first transport format;switching transmission transport format from the first format to asecond transport format; and transmitting, to the receiving apparatus, asecond frame in accordance with the second transport format and at asecond power level corresponding to the second transport format prior toreceiving a feedback from the receiving apparatus regarding transmissionpower level of the second frame, wherein the transmission of the secondframe occurs in a time frame after a time frame used for thetransmission of the first frame.
 2. The method of claim 1, wherein thefeedback comprises power control information.
 3. The method of claim 1,further comprising: determining the second power level to be higher fora data portion of the second frame than the first power level for a dataportion of the first frame.
 4. The method of claim 1, furthercomprising: determining the second power level to be the same for areference portion of the second frame and the first power level for areference portion of the first frame.
 5. The method of claim 1, furthercomprising: determining a data portion of the second frame requiring adifferent SNIR than a data portion of the first frame, therebytriggering the switch from the first transport format to the secondtransport format.
 6. The method of claim 5, further comprising:determining the second power level based on the different SNIR.
 7. Themethod of claim 1, wherein the second power level is a function of achange in a set point of a power control loop.
 8. The method of claim 7,wherein the set point comprises a target SNIR.
 9. An apparatus forcommunication, comprising: a transmitter configured to transmit, to areceiving apparatus, a first frame in accordance with a first transportformat and at a first power level corresponding to the first transportformat; and a controller configured to switch transmission transportformat from the first format to a second transport format, wherein thetransmitter is further configured to transmit, to the receivingapparatus, a second frame in accordance with the second transport formatand at a second power level corresponding to the second transport formatprior to receiving a feedback from the receiving apparatus regardingtransmission power level of the second frame, and wherein thetransmission of the second frame occurs in a time frame after a timeframe used for the transmission of the first frame.
 10. The apparatus ofclaim 9, wherein the feedback comprises power control information. 11.The apparatus of claim 9, wherein the controller is further configuredto determine the second power level to be higher for a data portion ofthe second frame than the first power level for a data portion of thefirst frame.
 12. The apparatus of claim 9, wherein the controller isfurther configured to determine the second power level to be the samefor a reference portion of the second frame and the first power levelfor a reference portion of the first frame.
 13. The apparatus of claim9, wherein the controller is further configured to determine a dataportion of the second frame requiring a different SNIR than a dataportion of the first frame, thereby triggering the switch from the firsttransport format to the second transport format.
 14. The apparatus ofclaim 13, wherein the controller is further configured to determine thesecond power level based on the different SNIR.
 15. The apparatus ofclaim 9, wherein the second power level is a function of a change in aset point of a power control loop between the apparatus and thereceiving apparatus.
 16. The apparatus of claim 15, wherein the setpoint comprises a target SNIR.
 17. An apparatus for communication,comprising: means for transmitting, to a receiving apparatus, a firstframe in accordance with a first transport format and at a first powerlevel corresponding to the first transport format; and means forswitching transmission transport format from the first format to asecond transport format, wherein the transmitting means furthertransmits, to the receiving apparatus, a second frame in accordance withthe second transport format and at a second power level corresponding tothe second transport format prior to receiving a feedback from thereceiving apparatus regarding transmission power level of the secondframe, and wherein the transmission of the second frame occurs in a timeframe after a time frame used for the transmission of the first frame.18. The apparatus of claim 17, wherein the feedback comprises powercontrol information.
 19. The apparatus of claim 17, further comprising:means for determining the second power level to be higher for a dataportion of the second frame than the first power level for a dataportion of the first frame.
 20. The apparatus of claim 17, furthercomprising: means for determining the second power level to be the samefor a reference portion of the second frame and the first power levelfor a reference portion of the first frame.
 21. The apparatus of claim17, further comprising: means for determining a data portion of thesecond frame requiring a different SNIR than a data portion of the firstframe, thereby triggering the switch from the first transport format tothe second transport format.
 22. The apparatus of claim 21, wherein thesecond power level is determined based on the different SNIR.
 23. Anon-transitory, processor-readable medium for communication, thenon-transitory, processor-readable medium comprising codes executableto: transmit, to a receiving apparatus, a first frame in accordance witha first transport format and at a first power level corresponding to thefirst transport format; switch transmission transport format from thefirst format to a second transport format; and transmit, to thereceiving apparatus, a second frame in accordance with the secondtransport format and at a second power level corresponding to the secondtransport format prior to receiving a feedback from the receivingapparatus regarding transmission power level of the second frame,wherein the transmission of the second frame occurs in a time frameafter a time frame used for the transmission of the first frame.
 24. Abase station, comprising: an antenna; a transmitter configured totransmit, to an access terminal via the antenna, a first frame inaccordance with a first transport format and at a first power levelcorresponding to the first transport format; and a controller configuredto switch transmission transport format from the first format to asecond transport format, wherein the transmitter is further configuredto transmit, to the access terminal via the antenna, a second frame inaccordance with the second transport format and at a second power levelcorresponding to the second transport format prior to receiving afeedback from the access terminal regarding transmission power level ofthe second frame, and wherein the transmission of the second frameoccurs in a time frame after a time frame used for the transmission ofthe first frame.
 25. The base station of claim 24, wherein the secondpower level is a function of a change in a set point of a power controlloop between the base station and the terminal.
 26. The base station ofclaim 25, wherein the set point comprises a target SNIR.